The invention relates generally to torque measurement and calibration for rotatable shafts. More particularly, the invention relates to torque measurement and calibration under static load conditions.
Apparatus for measuring torque on a rotating shaft, such as an engine drive shaft, are well known. One design that has been very successful is described in U.S. Pat. No. 3,548,649 issued to Parkinson. This apparatus uses two toothed wheels mounted to the shaft in spaced apart relationship. Each wheel has a plurality of axially extending spaced teeth that extend into spaces between the teeth of the other wheel, thereby forming an interlaced array of teeth. Each wheel is attached to the shaft at axially spaced locations so that the spacing between adjacent teeth varies as a function of the shaft torque. A monopole variable reluctance sensor is used to detect the teeth spacing as the shaft rotates.
In many applications, however, it would be desirable to measure static shaft torque. For example, if a static torque measurement can be made in a field site environment, the integrity of the shaft can be checked without having to spin the shaft. This is especially useful when the shaft is an engine drive shaft such as may be used with a gas turbine engine. Static load testing in the field can be used to obtain information such as modulus or twist of the shaft under static load, and this field data can then be compared to corresponding data obtained when the shaft was new, thereby providing information as to whether the shaft has yielded during field use.
The objectives exists, therefore, for a static load torque measurement apparatus and method for rotatable shafts that preferably can be used with a shaft installed in its normal operating environment.